Work-flows of patients from arrival at medical care facilities through post-operative recovery typically require a patient to be transferred among multiple supports on which the patient is transported and/or stabilized. For example, upon arrival at a hospital via an ambulance, a patient initially may be moved on a stretcher into the hospital. The patient then may be transferred to a hospital gurney and moved to an imaging room for assessment. In the imaging room, the patient may be transferred to an imaging table such as an x-ray table, and then returned to the gurney. Subsequently, the patient may be transferred to a patient bed while recovering or awaiting further evaluation, and/or the patient may be brought to an operating room (OR) and transferred to an operating table. Such extensive repositioning of the patient has numerous disadvantages, including a reduced ability to generally immobilize the patient, increased personnel requirements due to assisting or lifting the patient from one support to another, and even the potential for injuries to hospital personnel because of the lifting. Nevertheless, a standard patient support suitable for use in multiple hospital environments thus far has not been introduced because of the diverse design requirements that must be met for widespread application.
Patient supports used in ambulance settings, for example, must meet different standards from patient supports used in conjunction with imaging technologies. When transporting a patient in an ambulance, the patient must be immobilized so that further injury does not occur during transport. Some instrumentation may need to be supported, such as an intravenous (IV) bag, and this instrumentation may be coupled to the patient gurney. In contrast, in the imaging setting, many materials may not be present with the patient due to interference with the operation of the imaging equipment. Thus, the patient typically is supported on a tabletop or tray that is generally free of additional medical equipment. And, in some instances, several patient settings are needed at the same time, for example imaging while a patient undergoes surgery. It is clear that a patient support with generic use across many of the patient settings would be desirable. An explanation of the particular requirements of some of these settings thus is next introduced.
Various diagnostic imaging technologies are known for visualization of internal organs and structures. Computed axial tomography (CT), for example, is an x-ray scanning technique for producing cross-sectional images, while magnetic resonance imaging (MR) is a radiation-free technique that uses a strong magnet and radiofrequency waves to produce images in desired “slice planes.” During CT and MR procedures in the clinical or operating room setting, a patient is placed on a movable support that translates within a housing. Traditional CT and MR equipment includes a ring-type gantry, and the patient is moved within the gantry so that images may be acquired of the anatomical region of interest. CT is known to be particularly useful for volumetric imaging but also suffers from poor soft tissue contrast, while MRI offers multi-planar imaging with superior soft tissue contrast.
The use of CT and MR for intraoperative imaging and interventional radiology (e.g., performing minimally invasive, targeted treatments using imaging for guidance) previously has been limited because of the substantial challenges posed by the geometry and overall size of the imaging equipment. The donut-shaped, ring-type gantries of traditional CT and MR equipment, for example, are not easily accommodated in operating rooms, and can cause or suffer from various deleterious effects due to interactions with other equipment. However, advances in CT and MR equipment are permitting more widespread application in intraoperative and interventional applications.
Until recently, only simple procedures such as biopsy or aspiration of fluid were performed in these scanners, and the need for additional capabilities in the support or table was limited. However, dramatic improvements in the image resolution and the speed of image acquisition of modern CT and MR scanners, the development of software and tracking technology for instrument guidance that can correlate with the images, and the development of software that permits the integration of multiple imaging modalities has greatly stimulated the use of these scanners in therapeutic procedures where image guidance can improve safety and efficacy. Some of the new minimally invasive ablative therapies require high precision placement of the delivery probes, and the monitoring and documentation achieved with concurrent CT or MR imaging is essential. Also, some newly developed surgeries simply cannot be done without concurrent CT or MR image guidance.
In such imaging procedures, the movable imaging support typically is provided on a base or carriage that receives the support at a desired height. For example, as disclosed in U.S. Pat. No. 6,161,237 to Tang et al., assigned to Med-Tec, Inc., a table base or carriage is provided with a tabletop that is mounted for longitudinal movement upon side rails attached to opposite sides of the carriage.
Imaging supports for movement on a carriage may be generally featureless, and simply may be sized to accommodate patients of a given height, weight, and girth. The supports may form patient couches when, for example, radiotranslucent cushions are placed along the supports and attached for example using Velcro®. Such cushions may enhance patient comfort and also may be readily conformable to a patient's anatomical contours so that patient movement is minimized. Typically, such a scanning tray is formed of a polymer or composite and has a smooth, generally flush and featureless surface. The tray may be cantilevered and slides into the gantry, with movement of the tray controlled by imaging software so that elevational and longitudinal positions may be set as needed.
A single imaging support also may be used with multiple imaging systems, as disclosed for example in U.S. Pat. No. 6,782,571 to Josephson et al., assigned to GE Medical Systems. As described in the patent, mobile patient transport is provided, allowing for patient setup outside of imaging bays. A patient may be quickly transferred between imaging systems without lifting the patient, and a dual end docking of the patient transport allows in line motion of the patient between systems, thus minimizing patient disruption.
The surrounding geometry of the imaging equipment, along with the requisite patient translation during scanning, presents a challenge when performing invasive procedures that require or are benefited by having equipment that ideally should remain in a fixed relationship to the immobilized patient. For example, a typical practice is to hold medical instruments manually, rely on gravity, tissue structure and friction, and to improvise props using towels or other padding. However, as procedures are becoming more complex and, in particular, as CT and MR imaging equipment are moved into the operating room environment, there is a need for new approaches. Because of the needs of medical personnel conducting intraoperative and interventional procedures, new patient supports and associated components, and new instrument positioning and holding devices and methods are desired to address these needs.
A variety of modifications have been proposed or implemented for intraoperative procedures, particularly involving MRI. For example, it has been reported that patient tables may be modified to allow efficient transition between the MR scanner and the surgical pedestal, the tables may be tilted (Trendelenburg, reverse Trendelenburg), rotated/pivoted, elevated and/or lowered, and the patient can be translated past the outer edge of the scanner into the fringe field when scanning is not required. In addition, rigid skull clamps have been fixed to such a table. See, e.g., Daniel F. Kacher et al., “Design and Implementation of Surgical Instruments, Devices, and Receiver Coils for Intraoperative MRI-Guided Neurosurgical and Neuro Ablative Procedures,” Automedica (2001); G. J. Rubino et al., “Interventional Magnetic Resonance Imaging Guided Neurosurgery—The UCLA Experience with the First 100 Cases,” Electromedica 68—neuro 2000, pp. 37-46.
Also known is a hybrid system in which an MRI scanner is connected to a digital subtraction angiography (DSA) unit by a 2.8 meter connecting table for patient repositioning, the connecting table being disposed between a standard removable MR table and the angiographic unit table. The imaging units are installed in adjacent rooms that may be separated by a shielding door, thereby allowing patient access to either system. The special table and environment of the combined imaging suite, however, required a custom-built clinical setup. See Th. J. Vogl, “MR-Guided Interventions with a DSA-MRI Hybrid System,” Electromedica 68 (2), pp. 116-121 (2000).
Some materials suitable for use in patient supports and associated components for use in the operating environment are unsuitable for use in the imaging environment. Because a strong magnetic field is created during MRI, ferromagnetic metal objects (and many other magnetic objects) must be kept out of the proximity of the machine. Such metal objects may cause poor image resolution and result in image artifacts that can mask or be misinterpreted as pathology. Concomitantly, metal objects present a safety hazard to the patient due to their attraction to the magnetic source (e.g., becoming projectiles due to their attraction by the magnet to the vicinity of the scanner table). Thus, high carbon steel alloys and pure iron must be avoided. Carbon fiber, a radiolucent material that is essentially transparent to x-rays, often is used in the CT setting but not generally accepted for use with an MRI scanner.
Thus, even the design of a patient support for use in just two different settings—such as the OR and the MR imaging environment—must meet a variety of requirements particular to each setting.
Along with the need for a new support for a patient, a variety of additional new components and methods may be desired by the technician, physician or surgeon. For example, one possible advance that may be achieved by application of such new CT and MR equipment is respiratory gating.
It is well known that the chest and abdominal organs can move several inches during respiration. One resulting problem is that this anatomical motion can adversely affect data acquisition, causing so-called ghost, or motion artifacts and thus adversely affect image quality. This problem is traditionally managed by asking patients to hold their breath, or by halting respiration if it is controlled mechanically, during the acquisition of images. A second problem arises when interventional procedures are done because of the inability of a patient to precisely repeat a given breath. This repetition is essential for accurate image correlation with a patient's anatomy when he or she is moved out of the scanner. Thus, for safety and efficacy, it is desirable to employ some method for monitoring and recording respiratory position at the time of acquisition of the CT or MR targeting image(s) that can be used to repeat that same anatomic position at the time of instrument placement. Such an exercise defines respiratory gating. Techniques have been developed for synchronizing cardiac and vascular imaging with a phase of the cardiac cycle by using electrocardiography signals to time the image acquisition and thereby provide images with consistent positions of anatomical features and to allow more accurate minimally invasive procedures. A comparable, clinically practical, real time signal of respiratory phase or internal organ position that can be used with CT or MR has not been available to date. It is especially problematic in the patient who is breathing voluntarily and not intubated with an endotracheal tube where volume input may be controlled. Normal respiration is a complex mixture of diaphragmatic and chest wall movements that may vary from breath to breath. The result is that a similar breath may not result in a similar position of internal organs that move with respiration. New minimally invasive ablative techniques such as (RF) radio frequency and cryogenic ablation require very accurate probe placement to simultaneously allow effective treatment and avoid injury to surrounding structures. Accurate respiratory gating is essential for accurate instrument placement in organs or structures that move with respiration and, in many cases, is the sine qua non of these treatment modalities. One method of respiratory gating proposed herein is to use real time ultrasound to monitor the position of the diaphragm or an organ moving with respiration throughout a procedure. For example, as the patient holds his breath for the targeting CT image(s), a “snapshot” ultrasound image of the diaphragm or other surrogate organ is also obtained. The ultrasound transducer is held against the patient in a fixed position throughout the procedure by the instrumentation described in the present invention. The patient is then withdrawn from the scanner gantry and an angle of approach and entry point on the skin is chosen. The site is suitably prepped and sterile drapes are placed if not already done. Then, either on his own or with coaching, the patient is able to watch the real time ultrasound image and breathe to the point of perfect overlap or coincidence with the earlier “snapshot” image, and then hold his breath at that point while the instrument is placed. Ideally this will result in perfect correlation of the patient's real time anatomy with the previously obtained CT image. The clinical result will be fewer sticks to achieve the ideal placement of instruments, saving time and patient morbidity. The key to success using this method is that the ultrasound transducer must remain in an absolutely fixed relationship to the patient throughout the imaging and instrument placement phases of the procedure. The present invention makes this both possible and practical.
Thus, there is a need for technology that functions within the imaging environment and addresses the problems associated with respiratory gating.
The ability to choose points in space that can be fixed relative to the patient or some part of the patient's anatomy for holding instruments, medical support equipment and patient positioning devices in a desired fixed orientation and location is fundamental to surgical and medical practice. While standard operating tables, for example, may be fitted with a broad range of accessories and attachments to facilitate a wide array of operations, the versatility and convenience provided by such a standard operating table is currently unavailable for use during CT or MR imaging using the supports currently employed therewith.
There is a need for a system that can offer many of the functions of a standard operating table when a patient is on a scanner tray. There also is a need for accessories that cooperate with the scanner tray to increase the accuracy of targeting, instrument positioning and guidance in an imaging environment.
Finally, there is a need for a versatile emergency stretcher that can carry a patient through multiple medical environments during resuscitation, diagnostic evaluation and initial treatment without risking further injury to the patient or emergency personnel that may come from the physical handling that traditionally has been required.